Don't enforce text format on uncaught exception warning message

[dtorok]

Description of changes: Changing the warning message that's emitted when the user function raises an uncaught exception. This change addresses two problems with this warning:

• in Telemetry API the warning message arrives unquoted, making the event JSON invalid
• in CWL the warning message is always in text format, regardless of the log format configuration of the function

With this change

• the TelemetryAPI event will be a valid json
• the format of this warning message will match the format of any other logs the function produces

Target (OCI, Managed Runtime, both): both

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.